Call ajax in Footer.php in CI 3

assume that u have Controller User and there is method named user_info(){...} that serves your ajax request: 

PHP Code:

class User extends CI_Controller { 

    public function __construct() {

        parent::__construct();    
    }
    public function user_info(){//serves ajax request
        $this->load->model('user_model');
        $user_info = $this->user_model->get_user_info();
        //if your want return array:
        $data['user_info'] = $user_info;
        echo json_encode($data); //in your javacript code in your ajax request set dataType: 'json'

        // or if u want to return html data
        $this->load->view('user_info_view', $data);//in your javacript code in your ajax request set dataType: 'html'

        //if u want to return html in your as an array
        $data['user_info_html'] = $this->load->view('user_info_view', $data, true);
//in your javacript code in your ajax request set dataType: 'json'
        echo json_encode($data);
    }
}  


in your ajax request url: 'http.mysite.com/user/user_info'